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The present invention relates generally to obstruction assemblies for measuring fluid flow, and more particularly to an improved multi-stage variable orifice flow obstruction sensor having a resilient flow-limiting obstruction member and fixed flow orifice adapted to accommodate a wide range of fluid flow such that sufficient pressure differentials are developed thereacross at low, normal and high flow conditions to accurately measure such fluid flow therefrom.
The use of obstruction assemblies to measure fluid flows is well known. Generally, fluid is a term which includes both liquids and gases. Flow is defined as the volume of fluid crossing a given point in a certain amount of time. In this regard, fluid flow is typically stated in units such as gallons and/or liters per minute.
It is important to accurately measure fluid flow in certain applications. One such application is when mechanical ventilators are implemented on respiratory patients. As commonly known in that field, proper ventilation may only be provided to these patients based upon accurately measuring the inspiratory and exhalation air flow of the patient.
One common prior art device used specifically for this intended purpose is a fixed orifice flow obstructor. The fixed orifice flow obstructor typically comprises a rigid plate with an aperture or orifice passing through it. This flow obstructor is placed within an enclosed conduit (e.g., pipe, hose, etc.) such that the fluid flowing therethrough can be measured. The diameter of the orifice is smaller than the inside diameter of the pipe.
According to fundamental physical properties, the pressure of the fluid flowing through the flow obstructor is always less than the pressure of the fluid flowing through the larger diameter pipe upstream from the flow obstructor. The difference between these two fluid pressures is defined as a pressure differential. The value associated with the pressure differential is indicative of the fluid flow, that is, a large flow produces a large pressure differential whereas a small flow produces a small pressure differential. Thus, due to this distinct relationship formed between them, the fluid flow may be measured based on obtaining the pressure differential. However, such fixed orifice flow sensor devices are limited to certain flow ranges and fail to provide adequate pressure differential signals over a broad range of flow rates.
More recently, variable orifice flow obstruction devices have been introduced which attempt to provide sufficient pressure differential over a broader range of flow rates. Examples of such flow obstruction devices are shown in U.S. Pat. Nos. 4,993,269 (issued to Guillaume et al.) assigned to the subject assignee and 4,083,245 (issued to Osborn), the disclosures of which are expressly incorporated herein by reference. Put generally, variable orifice flow obstruction devices utilize a hingably connected cut-out flapper that bends open with increased fluid flow so as to increase the effective flow area. Though such currently known and available flow obstructors achieve their primary objective of measuring fluid flows, they all possess certain deficiencies which detract from their overall utility.
As illustrated in FIG. 9, perhaps the greatest deficiency of the prior art flow obstructors is the inability to accommodate both high and low fluid flows such that sufficient pressure differentials can be developed to measure the fluid flows therefrom. In other words, the prior art flow obstructors fail to provide sufficient resistance to high fluid flow rates or provide to change of resistance to low flow rates. Due to such deficiency, the required pressure differentials cannot be obtained throughout broad ranges of flow rates which lead to the further failure of providing accurate, or even estimate, fluid flow measurements (as shown in FIG. 9). Consequently, the range of fluid flows which these prior art flow obstructors can effectively partake in measuring the flows is substantially small.
In view of the above-described shortcomings of prior art flow obstructors, there exists a need in the art for a flow obstructor sensor which can develop pressure differentials throughout a broad range of fluid flows. More specifically, there exists a need for a variable orifice flow sensor capable of accommodating both high and low fluid flow such that sufficient pressure differentials are created to accurately measure fluid flow thereacross.
The present invention specifically addresses and alleviates the above-referenced deficiencies associated with the use of flow obstructors of the prior art. More particularly, the present invention comprises an improved multi-stage variable orifice flow obstruction sensor that can develop suitable pressure differentials throughout a wide range of fluid flow rates. This specific obstruction sensor is designed to effectively accommodate both high and low fluid flow so that sufficient pressure differentials can be created. Such pressure differentials may then be sensed and correlated via conventional pressure transducers as routinely utilized in the art to accurately measure fluid flow.
In accordance with a preferred embodiment of the present invention, the obstruction sensor comprises a flow-limiting obstruction member which is preferably fabricated from a resilient metallic material. The flow-limiting member is engaged within an aperture defined through the obstruction sensor. Preferably, this flow-limiting member forms a constant substantial parallel relationship with respect to the aperture when uninfluenced by a neighboring cover member and/or fluid flow. However, due to its manner of engagement with the obstruction sensor""s aperture and its resilient make-up, it should be noted that the flow-limiting member may be urged and/or bent/flexed along the direction of the fluid flow when influenced by the cover member and/or fluid flow.
In the preferred embodiment of the present invention, the obstruction sensor further comprises an anterior member which is preferably made from a substantially rigid metallic material. This anterior member is engaged to the obstruction sensor in a manner as to position the cover member between the anterior member and the flow-limiting member. The prescribed anterior member comprises an upper anterior member portion which protrudes into and partially blocks the obstruction sensor""s aperture. In this respect, the lower edge of the upper anterior member portion and the cover member collectively form at least one fixed flow orifice, preferably two.
In operation, the obstruction sensor of the present invention is adapted to accommodate a wide range of fluid flow and provide a sufficient pressure differential thereacross to accurately measure a broad range of fluid flow. More specifically, when the obstruction sensor is confronted by a low fluid flow possessing a velocity or rate that is inadequate to move the cover member, its fixed flow orifice(s). allow such fluid to flow therethrough (best shown in FIG. 8). Furthermore, when it is alternatively, confronted by normal/intermediate fluid flow having velocities or rates that are capable of extending, i.e., flexing or bending, the cover member along the direction of the flow (and hence towards the flow-limiting member), the obstruction sensor allows the fluid to flow through its variable sized orifice or aperture which is now exposed due to the extension of the cover member (best shown in FIGS. 4 and 5).
Moreover, when confronting very high fluid flow with rate that can fully extend the cover member to a generally parallel axis along the flow direction, the flow-limiting member may support and mitigate the cover member""s extension by applying a generally opposing force thereagainst (best shown in FIGS. 6 and 7). In this regard, the present obstruction sensor creates required pressure differential across the obstruction at broad rate ranges of the fluid flow so that accurate flow determinations can be made using conventional pressure transducers through which such pressure differentials may then be correlated to measurements of fluid flow.